Vacuum pump

ABSTRACT

A vacuum pump, comprising at least one pump chamber (7, 8, 23 to 26) and at least one chamber (3, 5, 27) adjoining the pump chamber. The vacuum pump is fitted with a gas ballast device to avoid damage being caused in the adjoining chambers by the gases being pumped, the ballast gas being delivered via the chamber adjoining the pump chamber.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a 371 of PCT/EP98/00288 filed on Jan. 20, 1998.

BACKGROUND OF THE INVENTION

The present invention relates to a vacuum pump, comprising at least onepump chamber and at least one chamber for a motor, drive, gear,crankshaft or the like, adjoining said pump chamber.

In many branches of industry, vacuum pumps of the kind affected hereneed to pump etching and/or toxic gases. These gases may enter intochambers adjoining the pump chambers, said chambers being generallyseparated by seals (shaft seals, labyrinth boxes etc.) from the pumpchambers. Etching gases give rise to corrosion or abrasions in thesechambers, resulting in premature wear of the bearings or damage to othercomponents located therein. Moreover, etching or toxic gases may passthrough the chambers adjoining the pump chamber into the atmosphere. Inthe semiconductor industry, the demand for dry vacuum pumps, i.e. vacuumpumps which are free of oil at least with respect to their pump chamber,is ever increasing. The reason for this is, that the processes which areperformed in vacuum chambers to which the vacuum pumps are connected,need to be protected against interfering hydrocarbons. The gases formingor employed in the semiconductor industry pumped by the vacuum pumpoften have the property of forming solids while they are beingcompressed to atmospheric pressure. Also deposits of this kind may causeharm in the chambers adjoining the pump chamber.

SUMMARY OF THE INVENTION

It is the task of the present invention to design a vacuum pump of theaforementioned kind so that the risk of damage in the chambers adjoiningthe pump chamber as well as escaping of etching or toxic gases from thevacuum pump is mostly reduced.

This task is solved through the present invention by equipping thevacuum pump with a gas ballast device and by feeding the ballast gasthrough the chambers adjoining the pump chamber. A vacuum pump designedaccording to the present invention has an outer gas ballast or purge gasinlet, and a gas inlet located directly at the casing of the pumpchamber. Located between outer gas inlet and gas inlet are one orseveral chambers in need of being purged adjoining the pump chamber. Ina pump designed as detailed, the gas entering through the gas ballastinlet has the effect of purging the chamber or chambers adjoining thepump chamber. If etching or toxic gases enter in to the chamberadjoining the pump chamber through seals which are not, or no longercompletely fulfilling their sealing task, then these gases are pumpedback together with the ballast or purge gas into the pump before beingable to cause damage or escaping into the atmosphere. A furtheradvantage of the present invention is, that the design engineer has moreoptions at his disposal regarding the choice for the location of theinlet for the gas ballast or purge gas. Finally, the gas inlet at thecasing of the pump chamber may be held open all the time, so that a lowpressure forms in the chamber adjoining the pump chamber. The risk oftoxic or etching gases escaping through leaks in the outer casing isthus further reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and details of the present invention shall beexplained by reference to the design examples depicted schematically indrawing FIGS. 1 and 2. Depicted in

drawing FIG. 1 is a two-stage rotary vane vacuum pump and

drawing FIG. 2 a four-stage piston vacuum pump.

DESCRIPTION OF THE INVENTION

The rotary vane vacuum pump depicted in drawing FIG. 1 comprises pumpchamber casing 1 and drive motor 2. The pump chamber casing 1 is locatedwithin pump chamber 3 formed by outer casing 4, the motor in motorchamber 5 formed by motor casing 6 which is flanged to the outer pumpcasing 4. Located in pump chamber casing 1 are the pump chambers 7 and 8with their rotors 9 and 10. The rotors 9 and 10 are fitted to motorshaft 11 which is supported by multiple bearings in pump chamber casing2 and which is sealed. The larger stage 7, 9 of the pump is the inletstage and it is linked to inlet 12. The outlet 13 is linked to outletstage 8, 10. Inlet stage 7, 9 and outlet stage 8, 10 are linked to eachother through bore 14. Bore 15 opens into this bore 14. Bore 15 islinked to pump chamber 3 and this bore is designated in the following asthe gas ballast or purge gas inlet close by to the pump chamber. The gasballast or purge gas inlet located outside the pump is designated as 16.It comprises valve 17 and constriction 18.

In the design example presented in drawing FIG. 1, the gas inlet 16 islocated in an area at the motor casing 6, remote of pump casing 4. Withvalve 17 open, i.e. during gas ballast or purge gas operation, the gasflows through motor chamber 5 and through pump chamber 3 to the inlet ofbore 15, which is the gas inlet located directly at the pump chambercasing. Gases escaping into the pump or the motor chamber throughleaking shaft seals are purged back into the outlet stage 8, 10. Ifrequired, baffles and/or several inlet ports 16 may be present so as toensure full purging of the chambers adjoining the pump chambers 7, 8.Moreover, an inert gas reservoir vessel may be connected to inlet port16, if there is a requirement for purging with an inert gas like N₂, forexample, or if a gas ballast is to be produced.

The ballast gas or purge gas inlet 15 close by to the pump chamber is atall times open in the direction of pump chamber 3. If valve 17 isclosed, a vacuum forms in pump chamber 3 and the motor chamber 5.Therefore gases entering through leaks in casings 4, 6 into pump chamber3 and motor chamber 5 can not escape to the outside. When valve 17 isopen, constriction 18 ensures that a low pressure is maintained in thecasings 4 and 6.

Depicted in drawing FIG. 2 is a four-stage dry compressing piston vacuumpump with its pump chamber casing sections 21 and 22 accommodatingcylindrically shaped pump chambers 23 to 26. Located between casingsections 21, 22 is the crankshaft chamber 27, the casing of which isdesignated as 28. The pistons 31 to 34 are each graded and form eightpump chambers which are in part connected in parallel so that the pumppresented has four pumping stages. Its inlet is designated as 35, itsoutlet as 36. In the older German patent application 196 34 519.7 avacuum pump of this kind is detailed. The last annular pump chamberforms the last stage of the vacuum pump presented. Its inlet isdesignated as 37, its outlet as 38.

The inlet 37 of the pump's last stage is linked via line 39 to thecrankshaft chamber 27. Its opening forms the gas inlet 41 close by tothe pump chamber. It is located in the vicinity of one face side ofcrankshaft chamber 28. Located in the area of the opposing side ofcrankshaft casing 28 is the gas ballast or purge gas inlet 16 with valve17 and constriction 18. Through the means already described inconnection with drawing FIG. 1, gas flowing in through gas inlet 16 maypurge the crankshaft chamber 27 and maintain a low pressure therein.

What is claimed is:
 1. A vacuum pump comprising:an outer casing; at least one pumping chamber disposed in an interior pumping chamber casing, said at least one pumping chamber having a proximate gas inlet disposed in said interior pumping chamber casing; at least one adjacent pump chamber adjoining said pumping chamber within said outer casing; and a gas ballast means for admitting ballast gas into said at least one pumping chamber through said at least one adjacent pump chamber; said gas ballast means including an inlet including a valve and a constriction disposed in said outer casing remote from the proximate gas inlet of said interior pumping chamber casing for selectively purging said at least one adjacent pump chamber when said valve is closed and in which said constriction creates a low pressure within said at least one adjacent pump chamber when said valve is opened when said pump requires gas ballast such that gas from said at least one pumping chamber is prevented from being released through said outer casing to the atmosphere.
 2. A vacuum pump according to claim 1, that further includes a plurality of gas inlets at several locations in the adjacent pump chamber.
 3. A vacuum pump according to claim 1, wherein the inlet of said outer casing is linked to an inert gas reservoir vessel.
 4. A vacuum pump according to claim 1, wherein said pump is a rotary vane vacuum pump.
 5. A vacuum pump according to claim 4, wherein said pump is a two stage rotary vane vacuum pump including a pair of pumping chambers constituting inlet and outlet stages disposed in said pumping chamber casing that further includes a bore that is connected to a linking bore passing between the inlet and outlet stages of said pump so that said linking bore communicates with the adjacent pump chamber.
 6. A vacuum pump according to claim 5, wherein an adjacent pump chamber includes an adjacent motor chamber and in which the gas inlet of said outer casing is provided in the motor chamber.
 7. A vacuum pump according to claim 1, wherein the pump is a multi-stage piston vacuum pump.
 8. A vacuum pump according to claim 7, wherein the proximate gas inlet of the last pumping stage of said multi-stage piston vacuum pump is linked to an crankshaft chamber in which said crankshaft chamber is the adjacent pump chamber.
 9. A vacuum pump according to claim 8, wherein said crankshaft chamber includes an inlet line extending to the last pumping stage and the gas inlet of the outer casing are arranged at opposing face sides of the crankshaft chamber. 